Implementing enhanced performance dynamic evaluation circuit by combining precharge and delayed keeper

ABSTRACT

A method and circuit for implementing enhanced performance dynamic evaluation, and a design structure on which the subject circuit resides are provided. The dynamic evaluation circuit includes a combined precharge and keeper device connected to a precharge node. The dynamic evaluation circuit includes control logic providing a control input to the combined precharge and keeper device. The combined precharge and keeper device responsive to the control input holds the precharge node precharged when the precharge node is not discharged early in an evaluate cycle.

This application is a continuation application of Ser. No. 14/574,571filed Dec. 18, 2014.

FIELD OF THE INVENTION

The present invention relates generally to the data processing field,and more particularly, relates to a method and circuit for implementingenhanced performance dynamic evaluation, and a design structure on whichthe subject circuit resides.

DESCRIPTION OF THE RELATED ART

A need exists for an efficient and effective circuit for implementingenhanced performance dynamic evaluation.

As technologies advance, performance continues to be a prime driver ofcircuit design innovation. Single thread performance especially for newprocessor products continues to be a critical metric for customers. Newcircuits are needed to continue to drive processor cycle time as fast aspossible.

FIG. 1 illustrates an example prior art dynamic evaluation circuit witha delayed keeper. A typical usage example would be a two-port StaticRandom Access Memory (SRAM) cell in which the evaluation devices includea stacked pair of N-channel field effect transistors (NFETs). A delayedkeeper is needed since the SRAM devices are small and cannot reliablyovercome a turned on keeper P-channel field effect transistors (PFET). Asecond stage evaluation circuit is shown with a global dot node toconnect or tie together multiple local dot nodes.

FIG. 2 shows typical waveforms for the prior art dynamic evaluationcircuit of FIG. 1. The delayed keeper receiving input PC Delay is turnedon only after the local dot node would have discharged. If the local dotnode discharged then the PC delay signal has no effect. If the local dotnode did not discharge then the PC delay signal will turn the localkeeper on, thus preventing the local dot node from discharginginadvertently due to leakage. The PC delay signal is timed such that theslowest possible discharge will happen before the delayed keeper turnson and the delayed keeper will turn on before the fastest leakagedischarge event could take place.

SUMMARY OF THE INVENTION

Principal aspects of the present invention are to provide a method andcircuit for implementing enhanced performance dynamic evaluation, and adesign structure on which the subject circuit resides. Other importantaspects of the present invention are to provide such method, circuit anddesign structure substantially without negative effects and thatovercome many of the disadvantages of prior art arrangements

In brief, a method and circuit for implementing enhanced performancedynamic evaluation, and a design structure on which the subject circuitresides are provided. The dynamic evaluation circuit includes a combinedprecharge and keeper device connected to a precharge node. The dynamicevaluation circuit includes control logic providing a control input tothe combined precharge and keeper device. The combined precharge andkeeper device responsive to the control input holds the precharge nodeprecharged when the precharge node is not discharged early in anevaluate cycle.

In accordance with features of the invention, performance of the dynamicevaluation circuit is enhanced by reducing device load from thesensitive precharge node which is the evaluation or local dot node ofthe dynamic evaluation circuit. Delay through the dynamic evaluationcircuit is reduced by the combined precharge and keeper device and thecontrol logic driving the combined precharge and keeper device fromdownsteam nodes that are less affected by extra load.

In accordance with features of the invention, the control logicproviding a control gate input to the combined precharge and keeperdevice includes a 2-input AND gate providing an input to a 2-input NORgate that receives a precharge signal at its second input. The AND gatereceives inputs of a set keeper delay signal and output of an inverterconnected to a local evaluation inverter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIGS. 1 and 2 respectively provide a schematic diagram representationillustrating an example prior art dynamic evaluation circuit andwaveforms for the prior art dynamic evaluation circuit;

FIG. 3 is a schematic and block diagram representation illustrating anexample circuit for implementing enhanced performance dynamic evaluationin accordance with a preferred embodiment;

FIG. 4 are waveforms illustrating operation of the example circuit forimplementing enhanced performance dynamic evaluation of FIG. 3 inaccordance with a preferred embodiment;

FIG. 5 is a schematic and block diagram representation illustratinganother example circuit for implementing enhanced performance dynamicevaluation in accordance with a preferred embodiment;

FIG. 6 are waveforms illustrating operation of the example circuit forimplementing enhanced performance dynamic evaluation of FIG. 5 inaccordance with a preferred embodiment;

FIG. 7 is chart illustrating performance measurements of the examplecircuits FIGS. 3 and 5 in accordance with a preferred embodiments forcomparison with the prior art; and

FIG. 8 is a flow diagram of a design process used in semiconductordesign, manufacturing, and/or test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings, which illustrate exampleembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In accordance with features of the invention, a method and circuits forimplementing enhanced performance dynamic evaluation, and a designstructure on which the subject circuit resides are provided. The dynamicevaluation circuit includes a combined precharge and keeper deviceconnected to a precharge node. The dynamic evaluation circuit includescontrol logic providing a control input to the combined precharge andkeeper device. The combined precharge and keeper device responsive tothe control input holds the precharge node precharged when the prechargenode is not discharged early in an evaluate cycle.

Having reference now to the drawings, in FIG. 3, there is shown anexample circuit for implementing enhanced performance dynamic evaluationgenerally designated by the reference character 300 in accordance with apreferred embodiment. Circuit 300 provides improvement over prior artcircuits, such as circuit 100, improving dynamic evaluation performance.

In accordance with features of the invention, circuit 300 implementsenhanced performance dynamic evaluation to speedup performance byreducing device load such as shown in FIG. 1, from the sensitiveprecharge node LOCAL DOT.

Circuit 300 includes control logic generally designated by the referencecharacter 302 provided with a combined precharge and keeper device 304connected to a precharge node labeled LOCAL DOT. The combined prechargeand keeper device 304 is a P-channel field effect transistor (PFET). Thedynamic evaluation circuit 300 includes a plurality of evaluationdevices 306 implemented by N-channel field effect transistor (NFETs),each receiving a respective evaluation input <0> through <N>, as shown.The PFET combined precharge and keeper device 304 is connected in serieswith the local evaluation N-channel field effect transistors (NFETs)306. The series connected PFET combined precharge and keeper device 304and evaluation NFETs 306 are connected between a voltage supply rail VDDand ground.

The control logic 302 provides a control input labeled PC LOCAL to agate of the combined precharge and keeper device 304. In accordance withfeatures of the invention, the combined precharge and keeper deviceresponsive to the control input holds the precharge node precharged whenthe precharge node is not discharged early in an evaluate cycle.

Circuit 300 includes an inverter 310 connecting the precharge node LOCALDOT to a second global evaluation stage. The control logic 302 includesan inverter 312 connected to the output of the local dot inverter 310, a2-input AND gate 314, and an OR invert gate or NOR gate 316. The ANDgate receives inputs of a set keeper delay signal PC DELAY b and theoutput of inverter 312, which is connected to the output of localevaluation inverter 310. The AND gate 314 provides a first input to a2-input NOR gate 316 that receives a precharge signal PC at its secondinput. The control logic NOR gate 316 provides a control gate input tothe combined precharge and keeper device 304.

The second global evaluation stage includes an N-channel field effecttransistor (NFET) 320 receiving an input from the local dot lineinverter 310 and connected to a global dot node GLOBAL DOT. A globalprecharge P-channel field effect transistors (PFET) 322 receiving aglobal precharge input PC GLOBAL is series connected with the NFET 320,which are connected between the voltage supply rail VDD and ground. Aglobal keeper PFET 326 is connected to the global dot node GLOBAL DOTand receiving a gate input of an output of an inverter 328 connected tothe global dot node GLOBAL DOT. The global dot node GLOBAL DOT goes tothe output of the dynamic evaluation circuit 300.

Referring also to FIG. 4, there are shown waveforms generally designatedby the reference character 400 illustrating operation of the examplecircuit 300 for implementing enhanced performance dynamic evaluation inaccordance with a preferred embodiment. The combined precharge andkeeper device 304 receiving input PC LOCAL is turned on only after theprecharge node LOCAL DOT would have discharged. If the precharge nodeLOCAL DOT discharged then the PC LOCAL signal remains high so that thecombined precharge and keeper device 304 remains off until the nextprecharge. If the local dot node did not discharge then the PC LOCALwill turn on the local combined precharge and keeper device 304corresponding the PC DELAY b input to AND gate 320 providing the low PCLOCAL, thus preventing the precharge node LOCAL DOT from discharginginadvertently due to leakage. The PC LOCAL signal is timed by PC DELAY bsuch that the slowest possible discharge occurs before the combinedprecharge and keeper device 304 would turn on and the combined prechargeand keeper device 304 turns on before the fastest leakage dischargeevent could take place responsive to the AND gate output and the PCsignal applied to NOR 316.

Referring also to FIG. 5, there is shown another example circuitgenerally designated by the reference character 500 for implementingenhanced performance dynamic evaluation in accordance with a preferredembodiment. Circuit 500 provides further improvement over prior artcircuits improving dynamic evaluation performance.

Circuit 500 includes control logic generally designated by the referencecharacter 502 provided with a combined precharge and keeper device 504connected to a precharge node labeled LOCAL DOT. The combined prechargeand keeper device 504 is a P-channel field effect transistor (PFET). Thedynamic evaluation circuit 500 includes a plurality of evaluationdevices 506 implemented by N-channel field effect transistor (NFETs),each receiving a respective evaluation input <0> through <N>, as shown.The PFET combined precharge and keeper device 504 is connected in serieswith the local evaluation N-channel field effect transistors (NFETs)506. The series connected PFET combined precharge and keeper device 504and evaluation NFETs 506 are connected between a voltage supply rail VDDand ground.

The control logic 502 provides a control input labeled PC LOCAL to agate of the combined precharge and keeper device 504. In accordance withfeatures of the invention, the combined precharge and keeper device 504responsive to the control input holds the precharge node precharged whenthe precharge node is not discharged early in an evaluate cycle.

Circuit 500 includes an inverter 510 connecting the precharge node LOCALDOT to a second global evaluation stage. The control logic 502 includesan inverter 512 connected to the output of the second global evaluationstage, a 2-input AND gate 514, and an OR invert gate or NOR gate 516.The AND gate 514 receives inputs of a set keeper delay signal PC DELAYand the output of inverter 512, which is connected to the output ofsecond global evaluation stage. The AND gate 514 provides a first inputto a 2-input NOR gate 516 that receives a precharge signal PC at itssecond input. The control logic NOR gate 516 provides a control gateinput to the combined precharge and keeper device 504.

The second global evaluation stage includes an N-channel field effecttransistor (NFET) 520 receiving an input from the local dot lineinverter 510 and connected to a global dot node GLOBAL DOT. A prechargeP-channel field effect transistors (PFET) 522 receiving a globalprecharge input PC GLOBAL is series connected with the NFET 520 andconnected between the voltage supply rail VDD and ground. A globalkeeper PFET 526 is connected to the global dot node GLOBAL DOT andreceiving a gate input of an output of an inverter 528 connected to theglobal dot node GLOBAL DOT. The global dot node GLOBAL DOT goes to theoutput of the dynamic evaluation circuit 500.

Referring also to FIG. 6, there are shown waveforms generally designatedby the reference character 600 illustrating operation of the examplecircuits 300 and 500 in accordance with a preferred embodiment forcomparison with the prior art. As shown, the circuit 500 has a smallerdelay at the precharge node DOT_500 than the precharge node DOT_300, andthe circuit 500 has a smaller delay at the global dot node GLOBAL DOT orGLB_500 than the global dot node GLB_300. Both circuits 300 and 500provide enhanced performance over the prior art, as shown.

FIG. 7 is chart illustrating example performance delay measurements ofthe example circuits 300, 500 in accordance with a preferred embodimentsin comparison with the prior art. As shown, the prior art delay inpicoseconds (ps) between evaluation to global dot is 45.26 ps, wherecircuit 300 or embodiment #1 has a delay of 44.69 ps for a 1.26%improvement, and circuit 500 or embodiment #2 has a delay of 43.83 psfor a 3.16% improvement.

FIG. 8 shows a block diagram of an example design flow 400. Design flow800 may vary depending on the type of IC being designed. For example, adesign flow 800 for building an application specific IC (ASIC) maydiffer from a design flow 800 for designing a standard component. Designstructure 802 is preferably an input to a design process 804 and maycome from an IP provider, a core developer, or other design company ormay be generated by the operator of the design flow, or from othersources. Design structure 802 comprises circuit 300, and circuit 500 inthe form of schematics or HDL, a hardware-description language, forexample, Verilog, VHDL, C, and the like. Design structure 802 may becontained on one or more machine readable medium. For example, designstructure 802 may be a text file or a graphical representation ofcircuit 300. Design process 804 preferably synthesizes, or translates,circuit 300 into a netlist 806, where netlist 806 is, for example, alist of wires, transistors, logic gates, control circuits, I/O, models,etc. that describes the connections to other elements and circuits in anintegrated circuit design and recorded on at least one of machinereadable medium. This may be an iterative process in which netlist 806is resynthesized one or more times depending on design specificationsand parameters for the circuit.

Design process 804 may include using a variety of inputs; for example,inputs from library elements 808 which may house a set of commonly usedelements, circuits, and devices, including models, layouts, and symbolicrepresentations, for a given manufacturing technology, such as differenttechnology nodes, 22 nm, 32 nm, 45 nm, 90 nm, and the like, designspecifications 810, characterization data 812, verification data 814,design rules 816, and test data files 818, which may include testpatterns and other testing information. Design process 804 may furtherinclude, for example, standard circuit design processes such as timinganalysis, verification, design rule checking, place and routeoperations, and the like. One of ordinary skill in the art of integratedcircuit design can appreciate the extent of possible electronic designautomation tools and applications used in design process 804 withoutdeviating from the scope and spirit of the invention. The designstructure of the invention is not limited to any specific design flow.

Design process 804 preferably translates an embodiment of the inventionas shown in FIG. 3 and FIG. 5 along with any additional integratedcircuit design or data (if applicable), into a second design structure820. Design structure 820 resides on a storage medium in a data formatused for the exchange of layout data of integrated circuits, forexample, information stored in a GDSII (GDS2), GL1, OASIS, or any othersuitable format for storing such design structures. Design structure 820may comprise information such as, for example, test data files, designcontent files, manufacturing data, layout parameters, wires, levels ofmetal, vias, shapes, data for routing through the manufacturing line,and any other data required by a semiconductor manufacturer to producean embodiment of the invention as shown in FIG. 3 and FIG. 5. Designstructure 820 may then proceed to a stage 822 where, for example, designstructure 820 proceeds to tape-out, is released to manufacturing, isreleased to a mask house, is sent to another design house, is sent backto the customer, and the like.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

What is claimed is:
 1. A method for implementing a dynamic evaluationcircuit having enhanced performance dynamic evaluation, said methodcomprising: providing a combined precharge and keeper device connectedto a precharge node of the dynamic evaluation circuit; providing controllogic of the dynamic evaluation circuit coupled to said precharge nodeproviding a control gate input to said combined precharge and keeperdevice; and said combined precharge and keeper device of the dynamicevaluation circuit holding said precharge node precharged when saidprecharge node not being discharged in an evaluate cycle.
 2. The methodas recited in claim 1 wherein providing said combined precharge andkeeper device connected to said precharge node of the dynamic evaluationcircuit includes providing a P-channel field effect transistor (PFET)implementing said combined precharge and keeper device of the dynamicevaluation circuit.
 3. The method as recited in claim 2 includesproviding said PFET combined precharge and keeper device connected inseries with a local evaluation N-channel field effect transistor (NFET),and the series connected PFET combined precharge and keeper device andevaluation NFET are connected between a voltage supply rail and ground,said evaluation NFET receiving an evaluation gate input.
 4. The methodas recited in claim 3 wherein said precharge node is a local dot node ofthe dynamic evaluation circuit and further includes providing aninverter connecting said precharge node to a global evaluation stage;and providing said control logic implemented by a 2-input AND gate, saidAND gate receives an input of a set keeper delay signal and a secondinput signal coupled from precharge node; said AND gate providing anoutput applied to an input to a 2-input NOR gate, and a precharge signalapplied to a second input of said NOR gate, said NOR gate providing saidcontrol gate input to said combined precharge and keeper device.
 5. Themethod as recited in claim 4 includes providing said second input signalto said AND gate coupled from a global dot node of the global evaluationstage of the dynamic evaluation circuit.